The trace amine, tyramine, has been implicated in a variety of human neurological disorders, including depression, migraine, schizophrenia and drug abuse. Although the role of tyramine in the CNS is poorly understood, the recent characterization of mammalian G-protein coupled receptors that can be activated by tyramine has aroused new interest in the role of tyramine in human physiology and disease. The long-term objective of this proposal is to understand how tyramine operates at the molecular, cellular, and neural circuit level to control behaviors. To this end, mechanisms of tyraminergic signaling will be analyzed in the simple nervous system of the nematode Caenorhabditis elegans. Our analysis has established that C. elegans has distinct tyraminergic cells and that tyramine regulates several behaviors. This project will use a combination of pharmacological, genetic, and electrophysiological techniques to understand tyramine function. Analysis of the pharmacological and expression profile of SHO-1, a novel ionotropic tyramine receptor isolated in our laboratory, will provide insight into how it modulates the output of distinct neural circuits. Behavioral analysis of sho-1 mutants, together with that of mutants for the G-protein coupled tyramine receptors ser-2 and tyra-2, should reveal how ionotropic and metabotropic pathways coordinately control tyramine dependent behaviors. Electrophysiological analysis of tyramine synaptic transmission at the neuromuscular junction should establish how tyramine affects postsynaptic properties. Lastly, an unbiased genetic screen will be conducted to search for mutants resistant to exogenous tyramine. Characterization of such mutants should identify novel signaling components and elucidate the signaling events downstream of tyramine receptors. These experiments will provide a multi-level perspective on how tyramine changes the output of neural circuits and controls animal behavior. Given tyramine's link with neurological disorders, these studies should ultimately accelerate our understanding of tyramine function in human physiology and disease. PUBLIC HEALTH RELEVANCE: Although the brain chemical, tyramine, is linked to a large variety of neurological disorders, including drug addiction, depression, attention hyper deficit disorders, Parkinson's disease, schizophrenia and headaches, little is known about its function. Since much of our understanding in human disease has come from studies of simple organisms like the round worm, Caenorhabditis elegans, we propose to study how tyramine controls behavior of this animal at the molecular and cellular level. Our studies will provide a better understanding of the functional role of tyramine in the brain, with the ultimate goal of treatment and prevention of human neurological disorders.